NXSLT1

This is what I've got.........A lil weiand 142 roots blower on a 96 Trans Am, OBD1 conversion bone stock motor except for headers and true duals. Running with the MAF, not speed density and a 2 bar map.

Here's my problem........everytime I go into boost, I mean the instant it sees boost I get knock, it basically pulls all my timing out and falls on it's face. I'm only running 5 lbs of boost and about 5* timing down low and 10* in the upper rpm. I read somewhere that the cobra mustangs didn't have knock sensors because the blowers made so much noise, this blower is pretty rattly, noisy. I've tried isolating the blower but that didn't do anything.

I was seeing IATs in the 140 range cruising and 190 range during the summer when I'd open it up for a couple seconds. I just built an intercooler last month and they are now about 115-120 cruising and when I open it up for a couple seconds the temps don't go up but I still get knock out the ***.

I've ran 102 unleaded thru it, still got knock. I've ran 105 octane E85 thru it for awhile, still got knock. I've had the heads off a couple times due to other issues and there is no sign of knock and there is no sign of knock on the plugs. I'm lost don't know what to do.

My big questions are........Should 105 octane be enough to kill any detonation if it was true knock?? Should this setup even run on a stock motor without knock? You gotta remember this is a roots blower, it's full on boost at any rpm soon as I hit the throttle, not a centrifugal that builds boost with rpm.

Anybody got any ideas???

edcmat-l1

iTrader: (10)

What are you tuning and logging with? How are you determining you're getting knock? I would assume your scanner is stating 'knock....yes', correct?
If you're using TC to tune, try upping burst knock enable %diff airflow threshold under 'constants' and see if that doesnt help.
BTW, with a roots style, I would recommend converting to the 2 bar and ditching the maf. The roots style builds boost much differently than the cent style, and are much harder to fudge a MAF/PE tune and make it run right.
If you decide to go 2 bar, shoot me a PM and I'll be glad to help you out. They're tricky on those old OBD1s with no 2 bar OS.

NXSLT1

I jacked that table all the way up so there is no way it can be getting burst knock. I'm using datamaster and tuner cat. It usually pulls the full 9* of timing when it sees knock, I haven't touched the knock settings. I'm using a 2 bar map with the maf. I halved the timing tables meaning at 50 kpa is where I start my boost timing. As far as cruising it does pretty good except it goes a lil lean on any kind of tip in, which is of course due to the boost of the roots and there is no "pumpshot" setting so the only way to take care of that is with the injector constatnt setting. But the problem with that is when I set the injector constant low enough to take care of the lean tip in then I can't take out enough fuel in WOT, runs pig rich, actually it almosts dies at that point.

Yes, I know roots blowers are full on boost where centrifugals build it with rpm. That's one concern because I see full boost down low in the rpm but I'm only running 5* timing from about 3500 and below and still see knock.

I'm gonna try a speed density tune here in a few days when I get it back together but I don't see it changing anything.

Should 105 octane be enough to tell if it's false knock or not??

edcmat-l1

iTrader: (10)

Yes, I would think 105 would be enough. But you may wanna try some 110 or 114. It'll probably kill the 02s though.
If you have access to an oscilloscope, scope the knock sensors, and if its got knock you'll "see" it.
Did you set it up to read the MAP properly? That is, the VE table?

NXSLT1

I haven't messed with the VE tables. I know there's some "controversy" over when it's referenced so I set them all to zero one time just to see and it had no affect on it whatsoever so I didn't waste any time on them. Of course if I go to speed density tuning then I'll have to tune them. I'm gonna see what's the highest unleaded octane I can get around here and try that, if I still get knock then I'll just detune the knock sensors til I can figure out how to quieten the blower down, that's the only thing I know to do at this point.

edcmat-l1

iTrader: (10)

If you detune the knock sensors, without verifying whether or not there's real knock, you risk doing catastrophic damage to your engine. Do you have forged pistons?
As for tuning in SD, it will most likely be your cure for the tip in lean condition.

NXSLT1

That's why I'm gonna get the highest octane I can get first.

edcmat-l1

iTrader: (10)

I dont think there's anything higher than 105 unleaded. May wanna set it up open loop, and pull the 02s for now, and run some real race gas in it.
Good luck, lemme know what you find.

jmalibuss

What is your Compression Ratio?
What plugs are you using (heat range specificly)

Well in a perfect world 5 lbs of boost should not have any detonation issues on 91 or 93 octane given the proper timing, plug heat range, plug gap, compression ratio and IAT. Even at 130* range you should be ok. I would be checking your plugs very often. If it is detonating then you will see it in the plugs. If you have not seen any signs of detonation when you had the heads off then it is probably hearing the blower noise. However, if it is hearing it at WOT then it most likey will hear it at part throttle. If you are using Datamaster to log with can you post up a log file so we can check it out?